1. Field of the Invention
The present invention relates in general to oxygen sensors, and more particularly to the oxygen sensors of a type that is suitable for sensing an oxygen concentration in an exhaust gas discharged from automotive internal combustion engines.
2. Description of the Related Art
Hitherto, various types of oxygen sensors have been proposed and put into practical use particularly in the field of automotive internal combustion engines.
One of such oxygen sensors is shown in Japanese Laid-open Patent Application (Tokkaihei) 9-178694. The oxygen sensor of the publication generally comprises a tubular casing that has an open base end, an oxygen detector unit that is installed in the tubular casing, a rubber bush that is plugged in the open base end of the tubular casing, and lead wires that extend from the oxygen detector unit to the outside of the tubular casing through the rubber bush.
In use, for measuring the amount of oxygen in the exhaust gas, the oxygen sensor is installed in the exhaust manifold or exhaust pipe which is highly heated under operation of the engine. That is, under operation of the engine, the rubber bush is kept subjected to a heat attack. Thus, usually, the rubber bush is made of a heat resistant type, the rubber bush is positioned away from the highly heated head portion of the tubular casing by increasing the length of the casing and/or the rubber bush is protected from the high heat by using a separate heat protecting member.